Read-write head positioning devices used in magnetic tape drives to align the read-write head with data in the magnetic tape often incorporate a two-actuator design. One actuator provides coarse positioning to move the read-write head between data bands. The other actuator provides fine positioning to maintain alignment between the read-write head and the data tracks. The two actuators are usually mounted in a "piggyback" arrangement with the fine position actuator riding on the coarse position actuator.
The coarse positioning actuator is typically a linear stage driven by a stepper motor. Stepper motors have the ability to move the linear stage anywhere across the width of the magnetic tape at modest speeds. However, most stepper motors lack the accuracy and bandwidth necessary to maintain alignment between the read-write head and the data tracks as the magnetic tape moves across the face of the read-write head.
The fine positioning actuator is typically a voice coil mounted on the linear stage and held at a rest position by some type of spring. A voice coil actuator provides micron to submicron precision positioning at a bandwidth of hundreds to thousands of hertz. However, a single voice coil and spring combination that can meet the fine positioning requirements across the full width of the tape is expensive and unnecessary.
The combination of coarse positioning and fine positioning is desired to meet the requirements associated with reading and writing on the magnetic tapes. Current solutions involve two actuators, their respective controllers, and a significant amount of hardware. What is desired is a simpler positioning device that requires only one actuator and minimal hardware.